The present invention relates generally to heating, ventilation and air conditioning (HVAC) systems for vehicles, and in particular to heating the air in such HVAC systems.
In a conventional HVAC module, an air temperature door (blend door) is used to direct the flow of air through or around the heater core after the air flows through the evaporator, and a mixing chamber is located downstream of the heater core to allow the air to flow through the heater core to mix with the air that flows around the heater core. This allows for a uniform temperature of the air flowing from the HVAC module by mixing the cooler air that flowed around the heater core with the warmer air that flowed through the heater core. However, with these conventional systems, the HVAC module may be larger than is desired due to the space needed for the blend door and the mixing chamber, and moreover the hot coolant is being continuously pumped through the heater core, whether needed or not.
Some have added a valve to stop the flow of coolant through the heater core when not needed. Others have employed a pump having pulse width modulation or on/off control in order to control the percentage of maximum coolant flow flowing through the heater core based on the current heating needs of the HVAC system. The pulsed width modulation is a linear flow control of the flowing coolant, with reduced flow when reduced capacity is needed and higher flow when higher heater capacity is needed. But these variations of the conventional system still do not overcome some of the drawbacks of the conventional HVAC module.